The invention concerns a device for fixing a tool, having a shank and a cutting part and preferably designed as a turning tool, to a holder having an insertion opening for accommodating the tool shank.
Fixing devices of the type specified at the beginning are intended to position and clamp a turning tool both axially and radially and in the circumferential direction. The holder is for its part inserted into a receptacle of a lathe or machining center and securely held there by means of a tool coupling. In the case of a known fixing device of the type stated, a tightening screw is provided in the holder and presses the prismatically shaped shank of the turning tool into a complementary prismatic receptacle. Good positioning in the circumferential direction is obtained as a result. The axial alignment is achieved by an axial stop, against which the turning tool is pressed during manual tightening. This type of handling during fixing is felt to be relatively laborious. Added to this is the fact that the insertion opening for the turning tool is not of a rotationally symmetrical design, with the result that different holders have to be provided for left-turning and right-turning tools. Owing to the stop inside the insertion openings that is necessary for the axial positioning, only single-cutting turning tools can be inserted into the holder and fixed to it.
On this basis, the object of the invention is to develop a fixing device of the type specified at the beginning which permits exact automatic positioning of the tool in the holder both in the circumferential direction and in the axial and radial directions, ensures high rigidity and nevertheless is easy to handle during the fixing operation.
The essence of the invention is that in the holder there is arranged a clamping element which is mounted in such a way that it can rotate to a restricted extent about an axis of rotation aligned transversely to the axis of insertion of the insertion opening and has a partially cylindrical surface portion which is eccentric in relation to its axis of rotation, and that in the shank surface there is arranged an open-edged, partially cylindrical recess which is aligned transversely to the shank axis and into which the clamping element can be screwed by its partially cylindrical surface portion, thereby fixing the tool shank and setting a position of the cutting edge that is defined with respect to the holder.
To be able to introduce the tool into the insertion opening easily when the clamping element is in the open position, it is advantageous if the clamping element has a top surface which, in its one turning end position, faces the insertion opening and exposes the latter for the passing through of the shank. For the precentering of the tool in the essentially cylindrical insertion opening, it is also advantageous if the cylindrical tool shank has an aligning surface which can be aligned parallel to the top surface and is parallel to the axis of the shank and the axis of the recess. If, in addition to this, the axis of the recess is aligned perpendicularly to the main cutting force acting at the cutting part, tools both for right-turning and for left-turning machining can be inserted into one and the same holder.
The eccentricity of the partially cylindrical surface portion is expediently dimensioned such that the surface portion comes into contact with the cylindrical surface of the recess and clamps the shank of the tool in the wall of the insertion opening when the clamping element is partially turned. The transverse alignment of the axis of the recess to the axis of insertion has the effect of achieving positioning both in the circumferential direction and in the axial and radial directions. Particularly high accuracy in longitudinal positioning is achieved if, in its fixing position, the clamping element bears with the partially cylindrical surface portion against the bottom of the partially cylindrical recess, of a slightly larger diameter, in such a way that the joining plane between the axis of rotation and the axis of eccentricity forms an angle of 3xc2x0 to 35xc2x0, preferably 5xc2x0 to 15xc2x0, with a radial plane of the tool shank that is perpendicular to the axis of insertion.
A recess for accommodating the clamping element is preferably arranged in the holder, which recess is concentric with respect to the axis of rotation, partially cylindrical, open-edged toward the insertion opening and, in the clamping position of the shank, is complemented by the partially cylindrical recess of the shank to form a full cylinder. Furthermore, according to a preferred refinement of the invention, an axial limiting stop for the tool is arranged on the holder, the recess being open toward the clamping element when the tool is bearing against the limiting stop, and it being possible during the fixing operation for the tool to lift automatically off the limiting stop counter to the direction of insertion, thereby setting a defined axial position of the cutting edge. The limiting stop is in this case expediently arranged in the insertion opening such that, in the direction of insertion, it is behind the clamping element. It may be designed, for example, as a pin, wedge or lug engaging in the insertion opening. Another configurational variant provides that the insertion opening is designed as a locating hole for the tool shank and the limiting stop is designed as an annular shoulder bounding the locating hole.
Particularly reliable fixing, which cannot be released during the machining operation, is achieved with the means according to the invention by the clamping element being mounted in such a way that it can rotate at both its ends at bearing locations of the holder and being able during the clamping operation to bend flexibly between the bearing locations, thereby producing a self-locking frictional connection and eliminating radial and axial shank backlash in the insertion opening. These measures additionally lead to a high positioning accuracy, since the clamping element in its flexibly bent fixing state is pressed to a greater extent against the wall of the recess near its extreme ends than in its middle. If it is additionally considered that the shank in the fixing state is pressed against the wall of the opening lying opposite the clamping element, three-point pressing contact with high positioning accuracy is obtained in the direction of fixing exerted by the clamping element on the shank.
The measures according to the invention make it possible for there to be formed on the end face of the shank lying at the opposite end from the cutting part a second cutting part, which when not in use can be introduced into the correspondingly lengthened insertion opening in the holder and protected there against destruction.
The handling of the fixing device according to the invention is made easier if the clamping element can be turned between a first end position, exposing the insertion opening for the passing through of the shank, and a second end position, forming a securement against turning for the clamping element in the holder, the end positions being defined by stops. The clamping element may for this purpose have on its one extreme end a head engaging in a turned relief of the holder, the stops being arranged such that they are outwardly covered by the head in a protected position within the turned relief. Furthermore, the clamping element may have at each of both its extreme ends a wrench socket, in order that it can be operated from both sides.
According to a further advantageous refinement of the invention, the tool holder is axially penetrated by a coolant duct. It is particularly advantageous in this case if, outside the portion accommodating the shank, preferably designed as a locating hole, the coolant duct is formed by the insertion opening and, within the portion accommodating the shank, it is formed by at least one axially parallel recess which is open-edged toward the insertion opening and additionally bounded there by the shank.